1. Field of the Invention
The present invention relates to tensionable cable bolts for use in strata support and has been developed especially, but not exclusively for cable bolts that are resin anchored prior to tensioning, tensioned, then post grouted with cement. However, it will be appreciated that the invention is not limited to this particular field of use and may also be applicable to other applications where improved strata support is desirable.
2. Description of Related Art
Roof and wall support is vital in mining and tunneling operations. Mine and tunnel walls and roofs consist of rock strata, which must be reinforced to prevent the possibility of collapse. Rock bolts, such as rigid shaft rock bolts and flexible cable bolts are widely used for consolidating the rock strata.
Known methods for reinforcing rock faces include the use of tensionable cable bolts that are configured to allow post tensioning grouting of the cable into a rock bore hole. These cable bolts are usually made from a plurality of steel filaments wound together to form a tendon. These tendons may also have a number of uniformly sized deformations in the form of, for example, “bulbs”, “cages”, “buttons” (sleeves), “swages” (rings or barrels that lock onto the cable using tapered cable gripping wedge elements) or other deformations along the length of the cable to provide improved anchorage and load transfer between the cable and the resin or cement grout and the strata. Bulbs and cages are formed by deforming at least some of the cable filaments so that they extend radially outwardly from the rest of the cable periphery. Buttons (sleeves) and swages are respectively crimped on and pressed on to the plain cable.
To facilitate post grouting of these types of cables, the bore holes must be oversized to thereby enable a breather tube and/or a grout tube to be inserted into the hole alongside the bolt and to allow the grout to flow freely into the bore. However, prior to installing the cement grout, the cable bolt is first point anchored with resin at the distal end of the bore.
In one form, point anchoring is achieved by locating a resin cartridge(s) in the closed end of the bore and then inserting and rotating the cable bolt to burst the resin cartridge(s) and mix its contents after which the mixed resin is allowed to cure. In another form, the cable bolt is pointed anchored by a mechanical anchor that expands in the bore. In yet a further form, the point anchoring may be a combination of chemical and mechanical fixing.
Once the resin is sufficiently set, the bolt is tensioned and cement grout can then be inserted, as required, in the remainder of the bore. Typically this is done by either inserting a grout tube along side the cable to a location just below the point anchor so the grout enters from the top and displaces the air in the bore, or alternatively by filling from the end by inserting grout from adjacent the bore opening and displacing the air in the bore via a breather tube that has an opening just below the point anchor. In some prior art cable bolts, the grout or breather tube is positioned centrally in the cable bolt. In either case, care must be taken to ensure the grout tube is not pinched, impeding flow therethrough of either air or grout.